In the technical field of cylinder head gaskets, the gasket constructions containing soft material have been increasingly replaced in recent years by gaskets substantially formed of sheet metal plates. One reason for this development is that the asbestos material usually used in conventional soft material gaskets is no longer used because of health and environmental reasons. Additionally, the suitability of soft material gasket constructions for modern high duty engines, i.e., engines charged with a turbo-supercharger, is subject to limitations because of their low durability and elasticity. Finally, metallic gaskets provide advantages over soft material gaskets also in view of disposal and recycling.
Metallic flat gaskets for combustion engines of today usually consist of laminates being composed of a plurality of layers of sheet metal plates. One problem of these gaskets is that due to the punctual introduction of the screw forces in the built-in condition, the cylinder head and cylinder block tend to warp so that the distance between cylinder head and cylinder block in the area of the combustion chamber holes is larger than in the area of the cylinder head screws. This problem occurs in particular with aluminum cylinder heads nowadays increasingly us ed in engine construction which have a lower material stiffness compared to the cylinder heads made of gray cast iron material. Accordingly, a simple laminate made of different layers of sheet metal plates does not result in satisfying sealing conditions because of its relatively low deformability and elasticity as compared to soft material gaskets.
Metallic gaskets most often contain elastic means in the area of the through holes to counter this problem. In general, these means are half-beads, beads or edgings in the sheet metal plates of the laminate, resulting in a linear elastic sealing around the through holes.
Another problem is that the gap to be sealed between cylinder head and cylinder block of a combustion engine is oscillating because of the fast pressure and temperature changes, and therefore the gasket is subjected to constantly changing pressures ("beating") particularly in the area of the combustion chamber holes. This effect reduces the durability of elastic means, e.g. beads, arranged around the cylinder through holes.
In EP-A-0 230 804, a generic metallic flat gasket containing a compensating plate within the sheet metal laminate is described. In the area of the gasket confining the sealing gap towards the combustion chamber, the edge of the compensating plate is folded back completely onto itself or onto an intermediate plate, thereby forming a compensating means or stopper. The formation of the stopper results in a compensating area within the laminate which is characterized by an overall greater thickness of the different layers compared to the rest of the gasket. The enlarged gap in the area of the combustion chamber holes caused by the screw torque is compensated by the stopper or the compensating area.
Additionally, the gaskets of EP-A-0 230 804 have an elastic outer plate having a bead, the bead being arranged adjacent to the compensating area around the combustion chamber hole.
With the above-mentioned gaskets an elastic sealing line is only obtained in the area of the beads of the outer plates outside the compensating area. In the fastened position of the gasket, the compensating area with the stopper prevents the complete flattening of the beads. However, in view of its function as a first sealing line, it offers no elasticity.
Accordingly, the bead of the outer plate may be exposed to combustion gases and residues when the beating effect occurs, which may adversely affect its sealing function. Accordingly, high screw forces or stopper projections need to be applied to minimize the beating effect, which may cause unwanted warping of the engine parts.
From the German utility model G 94 14 941, a further generic flat gasket is known. The gaskets described therein contain pre-edged intermediate plates having an elasticity due to the edgings. The edgings are located in the area of the beads of the beaded outer plates. Accordingly, the sealing lines that build up within the laminate after mounting of the gasket are not concentrating in defined functionally separated areas, but are distributed over different areas of the laminate.
Accordingly, one object of the present invention is to avoid the disadvantages of the prior art stated above. A further object is to provide metallic flat gaskets which achieve satisfying sealing characteristics in spite of their simple construction.
These and other objects are solved by the features of claim 1 and the depending claims.
The gaskets according to the present invention are metallic flat gaskets. This does not exclude that the gaskets comprise soft coatings, e.g. to enhance sealing properties. These coatings may be polymer coatings which are normally used for these purposes. Furthermore, the gaskets may contain elastomeric sealing elements at certain positions, for example rubber pads, e.g. for sealing of through holes for a cooling or lubricating liquid.
The gaskets according to the present invention are laminates made of layers of different sheet metal plates. Such laminates may comprise, for example, different sheets that are connected with each other by bordering of the edges of the sheets. The laminate may also be obtained by simply stacking different sheet metal plates on top of each other. The individual sheets of the laminate are then preferably held together by metal eyelets or by rivetting, clinching, gluing or welding. However, it is also possible to obtain the gasket laminate by stacking the individual plates on top of each other only during the mounting of the gasket. In this case, the alignment of the plates is done, for example, with the help of the cylinder bolts or fixing pins. The term "sheet metal plates" used in connection with the present invention also includes elements of the gasket laminate such as bordered metal sheets, metal rings (optionally beaded) or spring rings.